The organization of cells in the cat dorsal horn will be examined with regard to cutaneous input. Extracellular recording has been used to examine somatotopic organization of the hindlimb region, and to statistically analyze the relations among receptive field location shape, and size; spontaneous activity; central delay; and location of recording site. Two other subsidiary projects have also been completed: (1) a computer simulation study has shown that multiple dendritic trigger zones, all subjected to random excitatory input, cannot account for the spontaneous discharge patterns seen in LI-spinal cats; and (2) human psychophysical experiments reveal (a) better two-point discrimination across the dorsal midline than on either side of the midline; and (b) better two-point discrimination of stimuli oriented across the long axis of the limb than parallel to the long axis. These results are in accord with predictions based on anatomy and physiology of the somatosensory system. Intracellular recording, in conjunction with dye-injection, will be used to investigate correlations between physiological properties and cell geometry. Computer analysis of discharge timing will be used to analyze synaptic relations between afferent fibers and dorsal horn cells, as well as between pairs of dorsal horn cells.